The leading cause of coronary heart disease (CHD)is atherosclerosis of the coronary arteries, which is one of the most prevalent causes of morbidity and mortality in man. A major predisposing factor to atherosclerosis is low levels of high density lipoprotein-cholesterol (HDL-C). About half of the variation in HDL-C levels is due to genetic influences. Recently, a newly discovered gene, called endothelial lipase(EL), has been shown to have several unique features that make EL a prime candidate gene for low HDL-C and atherosclerosis. EL affects HDL metabolism in vivo, has high levels of phospholipase activity, is expressed by vascular endothelium, and is upregulated by inflammatory cytokines. The objectives of this project are to determine the genetic contribution of EL to variation in plasma lipid profile and to assess its role structurally and functionally. To achieve these objectives, the following specific aims will be carried out. 1) To identify and characterize mutations in the exons and intron-exon boundaries of the EL gene, molecular genetic techniques will be used in selected individuals expressing the extreme phenotype of high and low HDL-C levels. The impact of the discovered mutations on plasma lipid profile will be evaluated in two population- based samples of Hispanics (n=406) and non-Hispanic Whites (n=604) using statistical methods. 2) To build and characterize a refined 3D molecular model of EL, homology modeling techniques will be used and its structural features will be characterized. Mutant 3D models will be generated for all missense mutations identified in Aim 1 and compared with the wild type model for structural differences using molecular modeling techniques. 3) To assess the lipase activity of the mutations identified in Aim 1 and structurally assessed in Aim 2, in vitro mutagenesis, expression, and functional studies will be used. In summary, this comprehensive project will characterize EL with respect to its genetic, structure, and function in regulating plasma HDL-C levels and hence a major genetic risk factor for atherosclerosis. Understanding the molecular basis of risk factors in atherosclerosis may lead to new strategies for reducing the risk of coronary heart disease in the population.